Electrified vehicles (EV) are equipped with an energy storage device (ESD) that serves as a source of propulsion power for an electric drive system. Typically, an ESD is in the form of a high voltage battery having positive and negative high voltage bus rails that can be coupled to a power conversion circuit when the EV is being driven, and coupled to a charging apparatus when the battery is being recharged. A leakage detection system is typically coupled to the positive and negative voltage rails to detect ground faults caused by current leakage from a high voltage rail to a vehicle chassis. For example, a system can be designed to calculate a leakage resistance between a voltage rail and a vehicle chassis; when a calculated leakage resistance falls below a predetermined threshold, a fault flag can be set. A leakage detection system in a vehicle may operate while the vehicle is being driven, as well as when it is parked and being recharged.
Charging apparatus at electric vehicle service equipment (EVSE) can be equipped with leakage detection circuitry to detect ground faults caused by current leakage from either a positive or negative high voltage rail of an EVSE power source. When an EVSE-based leakage detection circuit is coupled to a vehicle-based leakage detection circuit, confounding effects can occur that can adversely affect the fault-detection capability of both systems. For example, the confounding effects can cause false alarms that problematically interrupt a charging process. In addition, confounding effects can mask actual ground faults, preventing their detection by either the on-board or the off-board detection system. As a result, a charging process can be allowed to proceed under fault conditions.
A possible solution to the confounding problem is to disable one of the leakage detection circuits during a charging process. For example, a vehicle-based leakage detection circuit can be disabled when an EV is coupled to an EVSE. However, it may be that a charging apparatus is not equipped with a leakage detection circuit configured to detect ground faults at an EV. In that case, disabling a vehicle-based detection circuit removes the capability to detect faults at the EV. Likewise, automatic disabling of an EVSE-based detection circuit may prevent detection of ground faults at the EVSE if there is no common ground connection between the EVSE and the EV. Thus, there is a need to know whether coupling of an EV and an EVSE couples two leakage detection circuits to the same voltage bus, and to each other. In addition, there is a need to determine whether and how a leakage detection circuit should operate to properly detect isolation faults while it is coupled to a second leakage detection circuit.